1. Field of the Invention
The invention relates generally to cutting elements (xe2x80x9cinsertsxe2x80x9d) used on rock bits such as roller cone rock bits, hammer bits and drag bits. More specifically, the invention relates to optimizing the toughness of an insert by lowering its hardness to increase the effective drilling life of the insert for its particular drilling application.
2. Background Art
Polycrystalline diamond (xe2x80x9cPCDxe2x80x9d) enhanced inserts and tungsten carbide (xe2x80x9cWCxe2x80x94Coxe2x80x9d) inserts are two commonly used inserts for roller cone rock bits and hammer bits. Roller cone rock bits include a bit body adapted to be coupled to a rotatable drill string and include at least one xe2x80x9cconexe2x80x9d that is rotatably mounted to the bit body. The cone has a plurality of inserts pressed into it. The inserts contact with the formation during drilling. Hammer bits are typically include a one piece body with having crown. The crown includes inserts pressed therein for being cyclically xe2x80x9chammeredxe2x80x9d and rotated against the earth formation being drilled.
The PCD layer on PCD enhanced inserts is extremely hard. As a result, the PCD layer has excellent wear resistance properties. While the actual hardness of the PCD layer varies for the inserts used in each of the foregoing bit types, each type of PCD has a common failure mode of chipping and spalling due to cyclical impact loading on the inserts during drilling. Conversely, the softer, tougher tungsten carbide inserts tend to fail by excessive wear and not by chipping and spalling. Therefore a need exists for inserts for roller cone and hammer bits that are optimized for resisting both wear and impact as encountered during drilling.
One aspect of the invention is an insert for a drill bit is disclosed which includes an exposed surface having a contact portion adapted to periodically contact earthen formation. The contact portion includes a polycrystalline diamond material having a hardness in the range of about 2000 HV to about 3000 HV.
In some embodiments, the insert is attached to a roller cone on a roller cone bit. In some embodiments, the insert is attached to a crown on a hammer bit.
In some embodiments, the polycrystalline diamond material includes a composite having a first phase material including polycrystalline diamond and a second phase material selected from the group of oxide particulates metal carbides, and metallic particulates, nitrides, and mixtures of thereof.
Another aspect of the invention is a rock bit including a body, at least one cutter rotatably mounted on the body, and at least one insert disposed in the at least one cutter. The at least one insert has an exposed surface having a contact portion thereon adapted to periodically contact earthen formation as the cutter rotates. The contact portion comprises a polycrystalline diamond material, which itself comprises a composite material. The composite material comprises a first phase material comprising polycrystalline diamond, and a second phase material selected from the group of oxide particulates metal carbides, and metallic particulates, nitrides, and mixtures of thereof.
In some embodiments, the polycrystalline diamond material has a hardness in a range of about 2000 to 3000 Vickers Hardness Units (HV).